In recent years, needs for electrophotographic color image forming devices has been increased, such as multifunctional printers, facsimile machines and printers. Color printing is required to reproduce color tones that are as high-resolution as and as sharp as photographs; therefore, there is a demand for color toners that are able to meet the request.
To meet the request for high resolution and high image quality, it is needed to reduce the particle diameter of colored resin particles and to narrow the particle diameter distribution range. Therefore, in general, a toner for developing electrostatic images is produced by carrying out a classification operation for removal of particles that are coarser than and particles that are finer than a predetermined particle distribution range (i.e., coarse particles and fine particles) and adding additives (e.g., external additives) as needed. Especially, since coarse particles contained in a toner cause defects in printed image quality (e.g., filming and white spots), there is a demand for a toner production method that is capable of efficient removal of coarse particles.
As a method for solving the above problems, a method for producing a toner for developing electrostatic images is disclosed in Patent Literature 1, in which coarse particles are removed from the toner for developing electrostatic images by use of a wind power sieving machine under a specific air flow rate condition, thereby carrying out a sieving treatment with almost no clogging of the sieve. In Patent Literature 1, it is mentioned that almost no clogging occurs in the sieving machine, and stable operation with an excellent product recovery rate is ensured by setting the flow rate of a first air (supplied to the sieving machine together with a mixture of toner base particles and external additives) and the flow rate of a second air (supplied from an air inlet disposed on a coarse particle collection side) in optimal ranges.
However, even by the production method of Patent Literature 1, the efficiency of coarse particle removal from the toner cannot be sufficient, and there is a demand for a method for producing a toner for developing electrostatic images, which has higher coarse particle removal efficiency.
Patent Literature 1: Japanese Patent Application Laid-Open No. 2007-79444